Car Brakes E-Book

Jon Lawes

• Herausgeber: Crowood
• Kategorie: Fachliteratur
• Sprache: Englisch

Seitenzahl: 204

Veröffentlichungsjahr: 2014

Beschreibung

Modern car braking systems are designed to a very high standard, but the need for the home mechanic to know how to maintain their braking system is as important as ever. Whether upgrading your brakes at home or for the race track, Car Brakes offers guidance on upgrading, repairing and maintaining car braking systems. With step-by-step instructions, the book covers the key principles of braking systems, both drum and disc; stripping and rebuilding disc and drum brakes, and the replacement of brake pads and callipers; rebuilding and maintaining handbrakes and how to install a hydraulic handbrake; replacing and repairing brake lights; upgrading your brakes and finally, fault-finding and safety tips. Fully illustrated with 121 colour photographs and step-by-step instructions.

Leseprobe

CAR BRAKES

A GUIDE TO UPGRADING, REPAIR AND MAINTENANCE

Jon Lawes

THE CROWOOD PRESS

First published in 2014 by The Crowood Press LtdRamsbury, MarlboroughWiltshire SN8 2HR

www.crowood.com

This e-book first published in 2014

© Jon Lawes 2014

All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopy, recording, or any information storage and retrieval system, without permission in writing from the publishers.

British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library.

ISBN 978 1 84797 675 8

Disclaimer Safety is of the utmost importance in every aspect of an automotive workshop. The practical procedures and the tools and equipment used in automotive workshops are potentially dangerous. Tools should be used in strict accordance with the manufacturer’s recommended procedures and current health and safety regulations. The author and publisher cannot accept responsibility for any accident or injury caused by following the advice given in this book.

CONTENTS

ACKNOWLEDGEMENTS

INTRODUCTION

  1  BRAKES: AN OVERVIEW

  2  DISC BRAKES AND CALIPERS

  3  DRUM BRAKES

  4  HANDBRAKES

  5  BRAKE COOLING

  6  BRAKE BIAS

  7  BRAKE LINES

  8  BRAKE PEDALS AND PEDAL BOXES

  9  MASTER CYLINDERS AND BRAKE FLUID RESERVOIRS

10  BRAKE LIGHTS

11  BRAKE FLUIDS

12  BRAKE SERVO SYSTEMS

13  ANTI-LOCK BRAKING SYSTEMS

14  ELECTRIC BRAKING SYSTEMS

15  SUSPENSION GEOMETRY

16  THE ULTIMATE UPGRADE

17  FAULT FINDING

APPENDIX: EOBD/OBD-II CODES (BRAKING SYSTEM RELATED)

INDEX

ACKNOWLEDGEMENTS

The following, arranged in alphabetical order, have been instrumental in the production of this book:

Ben Short of BS Motorsport for his advice and guidance, specifically with regards to driver training and vehicle dynamics

Continental/ATE for their advice and images

EBC Brakes for their assistance with advice and photographs

Eric Jacobsen for his help, photos and advice

Justin Westley for his help and good humour

John Goldsmith of Goldsmith and Young Ltd for his support and loan of facilities

Mark Richardson for his assistance with photos, friendship and support

Mike Simpson for his friendship and photographic assistance

Simon Crosse for his photographic input

Simon Sexton and Adam Gallaway for their hand-skills and experience in producing the technical sections

And of course my family for their tolerance.

INTRODUCTION

Modern domestic braking systems are designed to a very high standard, from those fitted to the most basic shopping hatchback to super-cars costing more than the average home. Due to the demands of the German Autobahn, even the most humble vehicle is capable of being brought from top speed to stationary in a respectable time and distance. Most modern cars, however, will object to doing this on a regular basis, which means that certain upgrades or modifications will need to be carried out for fast road, track or competition use. In this book I will guide you through some of the key operating principles of braking systems, the potential for upgrades, and choosing which will be most suited to your application.

SAFETY

Before starting any task, from a visual inspection right through to a complete strip and rebuild of the brakes, you must take stock of some important safety points.

THE CRITICAL NATURE OF BRAKING SYSTEMS

If you make a mistake during the install of something simple like a car stereo you may find it doesn’t work, or not in the way you expect. Possibly the worst case scenario could be a fire. The best thing to do if you don’t know what you are doing is to get in an expert, but you can mitigate most risks by simply preparing and doing research before you start.

If you make a mistake during the installation of braking components the consequences are suddenly much more severe. Although braking systems are on the whole quite simple, there are many tiny errors that could result in catastrophic failure. If you are not confident that you can carry out any of the tasks detailed in this book, then obtain competent assistance. There is no shame in asking for a fresh set of eyes to look over critical tasks, and in many industries, such as aviation, critical systems such as brakes usually require an independent check prior to being released to service after maintenance, just to ensure no mistakes have been made; after all, we are all human. If a seal is incorrectly installed on a brake caliper or master cylinder you could lose all pressure from the system, and on older single line set-ups this could mean a total loss of brakes. Don’t be afraid to check your work.

TIDINESS IN THE WORK AREA

Although it sounds obvious, it is startling just how many otherwise very professional workshops are actually quite cluttered and untidy. This increases the risk of losing components, trip hazards and, of course, the ingress of dirt and grime into systems that should be kept clean. Keep a clean work area, especially when dealing with braking components. There should be two distinct phases to stripping components: dirty and clean. The dirty phase is when all the grime from the road is removed, old seals disposed of and contaminated fluid drained. Only when the component has been fully stripped and all contaminants removed can the clean phase start.

CHEMICALS AND BRAKE FLUIDS

In UK industry COSHH regulations (Control of Substances Hazardous to Health) have been in place for many years, controlling the use of various chemicals in the workplace. Most usefully for the home engineer, this has meant that comprehensive data sheets are available for the various fluids and chemicals that we use regularly, either online or directly from the product manufacturers. These allow the home user to check exactly what sensible precautions should be carried out when using harmful agents, and also give the best advice on what to do if an accident takes place. These data sheets, known as COSHH Assessments, detail the correct fire-fighting techniques, action to be taken if swallowed or the material touches bare skin, and other vital information. It is indeed very sensible to make sure you are fully informed about any substance you may be using, especially when it may be that you require some specific form of personal protective equipment (PPE) that might not be immediately obvious. Today it is very easy to protect yourself from harm with the amount of information available, and sensibly priced PPE is easily obtainable online. It is easy to minimize the risk to yourself: why risk harming yourself?

JACKING

Naturally, to reach the brakes of a vehicle, in most cases you will need to jack the vehicle up. The safest way of doing this is on a four post lift, but as that is beyond the means of most people we need to look at sensible alternatives. As we are working on the brakes it makes sense that either a single corner or an axle-set (i.e. both front or both rear wheels) will need to be elevated. First ensure you choose a safe area to do this: firm, level ground where there is no risk of the stand or jacks sinking or becoming unstable. Use high quality jacks and stands, and inspect them before use. Most items sold in Europe now come with a TüV marking, a statement that the design of the component you are using has been assessed by the Technischer Überwachungs-Verein (Technical Inspection Association). This is an independent group of organisations who assess equipment and processes to verify that they have been designed in a safety-conscious manner. If the jack or stand you have purchased has TüV accreditation then it has been assessed as suitable for its intended purpose if used in conjunction with the manufacturer’s instructions.

All equipment, however, is capable of failing over time, through fatigue, misuse or damage. Inspect all lifting equipment before use, keep jacks topped up with the correct fluid, repair or dispose of any leaking equipment, and never use any item of lifting equipment that you have any doubts about. When jacking a single wheel on a vehicle, which has been suitably chocked to prevent it from moving, use either the standard jacking point on the car for that corner or choose a sturdy part of the vehicle sub-frame or chassis. It is easiest to slightly loosen the wheel nuts while the vehicle still has weight on the wheels. You should not jack on components that may deflect, become damaged or move in relation to the rest of the vehicle, such as steering arms or anti-roll bars. Ensure the jacking pad is not going to slip and is correctly designed for lifting a vehicle without damage. Remember that a vehicle raised too low will be difficult to work with, and a vehicle jacked too high will be less stable, so a suitable compromise must be found. Once the vehicle is slightly higher than the required working height you can lower it onto a suitable support. Do not use bricks as they can crumble, potentially causing the vehicle to fall. Ideally an axle stand with a very wide base should be used, capable of safely supporting the vehicle’s weight while it is being worked upon. It is one thing to support a car’s weight but entirely another to support that weight plus the additional forces to which it will be subjected while trying to undo stiff bolts or levering components.

BRAKE DUST

The most harmful materials that were formerly present in friction materials are usually absent from modern cars, although asbestos can sometimes be found even on relatively new vehicles. The dust generated by brake pads, however, is still not healthy to inhale. By its very nature the friction material is designed to degenerate slowly, in order that it doesn’t break down rapidly during use, but the knock-on effect is that it will also hang around in your lungs for a long time. You can do some things to minimize the presence of dust, such as pressure-washing the area before you start, or damping down the area with a hand-held sprayer to keep the dust from becoming airborne. The best defence, however, is always to use the correct breathing protection to intercept the particles before they have a chance to enter your lungs.

BRAKE FLUIDS

Brake fluid is possibly the most flammable fluid in the entire car. As its very purpose is to operate in a high pressure pipeline it is often heavily compressed: a small leak will become a very fine spray capable of ignition purely due to its low flashpoint and the presence of hot materials in the engine bay. The exhaust manifold will easily generate enough heat to ignite a spray of brake fluid, with terrible consequences. Leaks in brake fluid systems are not dangerous just because of the reduced efficiency of the brakes, almost certainly leading to system failure, but because the fluid released has a high potential for causing a fire that could destroy the car. Ensure all unions and couplings are correctly made to a high standard, and any leaks are dealt with straightaway. Inspect systems for leaks regularly and never introduce any source of ignition when brake fluid is open or present.

Ensure you have a way of putting out brake fluid fires in the workshop: either CO2 or dry powder extinguishers can be selected. Remember that blasting a fluid with a high pressure extinguisher could just be a way of blowing the burning debris around the workshop, so take care before squeezing the trigger. Ensure all brake fluids are stored safely; partly because of the risk of fire, but also because brake fluid is poisonous and absorbs water from the air once opened. Only buy as much as you need and dispose of any leftover brake fluid soon after it has been opened. While many fluids are unlikely to damage paint, it is still quite possible, so wipe away any spilled fluid immediately and irrigate with water. Always read the relevant COSHH data sheet so you know what to do if it comes into contact with your skin. This may vary, depending on exactly what is contained within the fluid.

TESTING AFTER WORKING ON THE BRAKES

The first run after the installation of a braking component or overhaul of the braking system is going to be crucial. This should be carried out on a dry day, so you can see any moisture indicating leaks. It will also allow you to test the braking ability on a road with the maximum friction, working the brakes as hard as it is safe to do so. Once the system has been fully inspected to ensure there are no leaks, the pedal should be depressed with the engine running to ensure the servo (if fitted) is giving maximum assistance. Press as hard as you would during an emergency stop; it is better that a weak seal or union fails now than once you are moving. After depressing the pedal hard a few times, stop the car and inspect every single disturbed joint, seal and union for any signs of leakage. Use a cloth to dab against the areas to more visibly show the presence of leaking fluid, and inspect the seals on the calipers for signs of ballooning.

Only then can a low speed road test be carried out where no members of the public could be harmed in the event of a brake failure; farmland or similar, with the landowner’s permission, is ideal. By gently accelerating the vehicle a few times to a low speed, under 30mph, and then bringing it to a stop, you will be able to assess whether the vehicle is pulling up straight and true, and with a sensible amount of braking effort. If excessive effort is required, you may need to reassess your installation to confirm that it has been carried out correctly. Some pad materials do not work effectively while cold, or before they have been effectively bedded in. This means a certain period of on-road or on-track testing may be required before they can be said to be fully serviceable. Don’t forget to check that the handbrake is working correctly as well; it is your backup in the event of a main braking system failure. Don’t make this the last check you carry out on the system; after running the car for a few miles of use, repeat the same visual checks to ensure no leaks have developed, and check that the fluid level has not decreased. As the pads bed in there will be a slight drop in the fluid level, but this should be comparatively minor.

CHAPTER ONE

BRAKES: AN OVERVIEW

Braking, although based on firmly set scientific principles, seems to be shrouded in confusion and misleading information. Any highly regarded professional in the field, if asked whether there are any specific techniques one should use for setting up a braking system, tends to answer, ‘suck it and see’. There are so many factors that affect how the brakes work: the effectiveness of your tyre compound, air temperature, ride height, damping rate, even just moving a component in the car can change the braking to a significant degree. Because of this complex interaction, getting an effective braking system to work at its best can, to a certain degree, sometimes be more of an art than a science. We can give ourselves the best possible chance of getting it right first time, however, by understanding the principles and how they make a difference to the way the brakes decelerate the car.

Brakes have an unusual potential for being ‘sexy’ a number of times I have seen brake calipers fitted to vehicles purely for their aesthetic appeal, being completely unsuited to the application in hand. Proceed with caution: upgrades should be carried out only to the level that suits your needs. A vast increase in brake size will usually result in an increase in unsprung weight, with all the handling penalties that this incurs. Braking systems can also be costly, not only to install but to maintain. Consider carefully just how much braking you actually require. As a guideline, if you are not suffering brake fade and can easily lock the wheels, then you probably have enough braking for your needs.

Whether it is a friction block applied directly to the wheels or road, a six piston competition caliper on a ceramic disc or an air-brake, any system used to decelerate a vehicle is considered a braking system. The lineage of even the most modern systems can be traced quite clearly to the same systems fitted to the earliest automobiles, and this is because the basic principle was robust and simple in its application. Braking can be considered an energy conversion process: the forward motion of the vehicle is turned, via friction, into heat. Heat is the primary limiting factor with most systems. The ability to dissipate heat is often what dictates just how much braking the vehicle can do. However, the factor of traction on the road surface is too important to ignore; the most powerful brakes are useless if they lock instantly without gripping to the road.

PADS

It is almost too obvious to suggest that pads should be the first port of call when upgrading a system, but when modern road cars make the transition to track cars, just changing the pads is sometimes the only modification required. Compounds designed for higher temperatures are available to suit almost every vehicle on the market and the compromises that high specification pads used to impose on the driver have almost entirely been eliminated. High temperature pad materials used to work only when the disc and pad was up to temperature, but most high spec friction materials now work very adequately from cold. Selecting a pad material depends on the weight of the car and the type of driving intended. Certain circuits, for example, are very heavy on the brakes, requiring frequent heavy braking and few opportunities to allow the brake assembly to cool. In this scenario a pad that operates at a high temperature is best, although it can be difficult to determine exactly what these temperatures can be. During testing it is possible to return to the pits and apply an infrared thermometer to the discs, but this only tells you what the temperature is once the car has already started to cool.

A more reliable technique is temperature sensitive paint, which is applied to the edge of the disc and changes colour depending on the temperature reached. A typical paint kit, for example, might give temperature ranges from 300 to 650°C. The paints would come in three or four different colours, depending on the temperature they represent, and would be applied in small strips around 1cm long. After a test session the paint is checked, and any colour that has bleached to white represents a heat level exceeded: for example, a disc painted with red, yellow and green paint returning to the pits with white, white and green paint remaining has exceeded the temperatures represented by red and yellow, which could be 400 and 500°C respectively. The unchanged green paint could represent 600°C, meaning you would need to find a pad material capable of resisting fade up to a maximum of 600°C. Some manufacturers actually incorporate temperature sensitive paint into their pad production process, coating the metal backplate in a paint that discolours when the peak operating temperature has been exceeded. Bear in mind that ambient temperature, track temperature, humidity and other variables may affect the readings; just because a pad material suits one circuit, it does not mean it will be suitable for others.

Pad wear rates vary drastically depending on the compound and use. For this reason, if you are using a pad with which you are unfamiliar, it is prudent to monitor the wear more closely than usual.

Excessive wear due to the use of an incorrect pad compound, resulting in a melted piston and warped backing plates. ERIC JACOBSEN

Pads come in a confusing array of compounds and materials, with different levels of bite, wear resistance, heat resistance, dust production and noise level. A few of the materials used are listed here. The pad material is probably the most rapidly evolving part of the braking industry, so this list reflects only a very small section of a very complex area, and each manufacturer’s pad is likely to consist of a complex blend of these products:

•  Asbestos was used in brake pads owing to its excellent resistance to heat. It is rarely used today because of its carcinogenic properties, but can still be found on older vehicles.

•  Aramid is a contraction of the term Aromatic Polyamide, a synthetic fibre used as an alternative to asbestos. The Nomex material used in race-suits is an Aramid fibre, as is Kevlar.

•  Ceramic pads are perceived as quieter than their rivals since the frequency at which they squeal is usually beyond the frequency range of the human ear. They are generally more expensive than metallic pads, but kinder to the brake disc. They provide aggressive stopping power, good fade resistance and are lighter than metallic pads, making them ideal for competition. They tend to produce less dust, and the dust that is produced is lighter in colour and generally less noticeable. Because the temperatures generated are usually higher, and the pad does not conduct the heat away very effectively, a good quality disc should be used as it will be subjected to severe heat if used in competition.

•  Metallic brake pads tend to be slightly noisier than the other types due to the metals used in their construction. They are more aggressive to the disc than organic pads, relatively heavy, and often used as standard equipment due to their lower cost.

•  Organic is a term commonly used to designate a pad as being made of something other than metallic or ceramic compounds. Kevlar pads are considered to be organic. They are usually softer and less hardwearing than their ceramic or metallic equivalents.

•  Polyacrylonitrile is a synthetic polymer resin, and yet another modern alternative to asbestos.

•  Sintered pads are a variation on the metallic pad where the metal compounds are fused together during the manufacturing process at a temperature below the melting point of the metals used. Other materials may be added to sintered pads that are not employed with metallic pads. These include compounds or materials added to alter their wear and abrasion characteristics. Sintered pads tend to sit above organic and metallic pads, but below ceramic pads in their braking power and fade resistance. They usually use copper as the base material bonding the others together, contributing to their increased cost over organic pads.

Some calipers use more than one pad, meaning different compounds of friction material can be used together to achieve a hybrid stopping ability tailored to the type of competition you are engaging in.

If you notice squealing or poor performance, especially from new pads, it is possible that the disc and pad may have glazed. Disc and pad glazing can occur when the resins binding the pad materials together collect on the surface of the friction material and crystallize, forming a smooth surface that does not grip the disc effectively. It is for this reason that most pads have a bedding-in period, which allows the excess resin to be boiled off. Manufacturers tend to have different bedding-in procedures depending on the intended use. A road car application, for example, might simply suggest that the brakes are only used gently for the first few hundred miles. A racing pad manufacturer might suggest a few high speed stops separated by long cooling periods, allowing the resins to be heated and then gaseously dissipate through the gap between the pad and disc before they get a chance to crystallize. No matter which procedure you use, the basic principle is designed to avoid constant application of heat and pressure, which will cause the resins to glaze. In the event that the pads do glaze up, it is sometimes possible to remedy the situation by gently removing the glaze from the surface with a mild abrasive paper. Do not apply any liquid solution to the pad other than brake cleaning solvent and lightly abrade without causing damage to the surface. In the event that the pad starts to break up or crumble, it should be discarded along with the rest of the pads in the set. The rotor should also be very gently abraded using a fine grit paper evenly across its surface, as the resin will have transferred to the metal. Do not use an aggressive machine for this; hand pressure with an even effort across the whole surface is the best technique. Rinse with brake cleaner to remove any contamination once you have finished.